Robin wrote:

For fluorescent lamps, it is 3 hours "on" per switching.
I presume CFLs are the same, but I don't know that for sure.

I think that for CFLs it effectively assumes for the survival factor 2
hours if the start-up time is less than 0.3 seconds. That's due to
improve to 1 hour. This and a lot else about required perfomance is
specified for CFLs in Annex II, Table 4 to Commission Regulation (EC)
No 244/2009. And yes I am very sad that I could be bothered to look
up the source.

In practice they can be viable even when they arent on for anything like that long.

I used to use an incandescent for the bed head and those never did last all that long.

Then when I automated the lighting system in the house, I used a soft
start for that light, because that was free once the light was automated.

And I chose to have it come on at reduced intensity so that when you
turn it on in the middle of the night etc, you dont get dazzled by it. The
combination of those two saw the incandescent bulbs last for a very time.

Then my country, Australia, was actually stupid enough to ban
normal incandescent bulbs. And the electricity supply operation
handed out a box of free CFLs to anyone who wanted a box of them.

So I put one of them there, just to see how long they lasted, so I could see
if I needed to have a stash of incandescents that would last as long as I did.

Turns out that the CFLs last just as long as the incandescents do and
since they are a much softer light, you dont need bother to dim them
when you turn them on in the middle of the night etc. The light normally
isnt on for more than a few minutes every time its turned on, I dont
read in bed anymore, I prefer to read not in bed now.

I almost always get up in the dark, even in summer.